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Why All the Fuss Over Fiber?

When thinking about starting the carnivore diet, one of the first questions people ask is, “Where will I get my fiber?” This is based on our conception that fiber is good for us and that our bodies need to process fiber in order to function properly. We’ve all heard of a “high fiber, heart-healthy diet” or been told that “an apple a day keeps the doctor away.”

However, similar to other popular nutritional advice, science does not support the claim that fiber is healthy, necessary or even beneficial. Keep reading to learn where the fiber myth originated, why conventional advice about fiber is inaccurate, and how much fiber – if any – you should be eating per day.

What is fiber?

Fiber is a carbohydrate composed of indigestible plant matter that is further categorized as soluble and insoluble. Soluble fiber can be partially dissolved by water while soluble fiber cannot. Despite this distinction, by definition, the body cannot fully digest fiber, which leads many people to believe that it moves through the colon “sweeping” other waste matter along to its inevitable exit out of our bodies. 

How much fiber do we need?

Believe it or not, the answer is none. According to the 2015-2020 Dietary Guidelines for Americans, an essential nutrient is defined as “a vitamin, mineral, fatty acid, or amino acid required for normal body functioning that either cannot be synthesized by the body at all, or cannot be synthesized in amounts adequate for good health, and thus must be obtained from a dietary source. Other food components, such as dietary fiber, while not essential, also are considered to be nutrients.” 

Not convinced? Well, if you’ve been following a low-carbohydrate diet, then you may be familiar with the following statement from the Panel on Macronutrients: “The lower limit on dietary carbohydrate compatible with life apparently is zero, provided that adequate amounts of protein and fats are consumed.” If fiber is a subset of carbohydrates, then we don’t have a need for fiber, right? 

Unfortunately, convincing most people why fiber is unnecessary is not as simple as this logic. Our medical and lay community is filled with high-fiber recommendations and conflict with the Panel’s. Let’s take a closer look. 

Where did high-fiber recommendations come from?

High-fiber recommendations originated in the 1970s based on observations of Ugandan populations by Dr. Denis Burkitt. He compared their disease patterns to Western diseases and concluded in the British Medical Journal that many Western diseases –  such as coronary heart disease, diabetes type II, colorectal cancer, obesity, and hypertension –  were the result of Western diet and lifestyle. His book about fiber became an international bestseller and led to the now widespread conventional advice that low-fiber diets cause disease.

Why Burkitt’s simplistic approach was readily and widely accepted is unclear. But it has led many to believe that necessary for digestion and is protective again colon cancer, heart disease, and digestive issues. According to human physiology and research studies, does increasing fiber increase our overall health? 

Don’t we need fiber to break down undigested carbohydrates?

A lot of people will argue that we should eat copious amounts of fiber to break down carbs. But let’s take a look at what fiber does once consumed – it is broken down into short-chain fatty acids, namely propionic acid (propionate), acetic acid (acetate), and butyric acid (butyrate), which is the fuel source preferred by the large intestines endothelial cells. 

But you don’t need to eat fiber to get butyrate. In fact, butter is the best dietary source of butyrate and it doesn’t require carbohydrate consumption. There is no need to consume glucose, fructose, and/or processed foods to realize the benefits of butyrate for digestion. 

Does fiber reduce the risk of colon cancer?

In 2005, a study was published that aimed to get to the bottom of inconsistent observational findings related to fiber and colon cancer. Researchers followed 725,628 men and women involved in 13 other cohort studies for 6 to 20 years to determine which individuals had higher incidents of colorectal cancer. While dietary fiber intake was inversely associated with the risk of colorectal cancer in age-adjusted analyses, after accounting for other dietary risk factors, high dietary fiber intake was not associated with a reduced risk of colorectal cancer. Similar to other nutrition-based research, other factors were at play. 

Fast-forward to 2017 and researchers still do not have strong evidence. This study systematically reviewed five studies of over 4000 subjects. Researchers concluded there was no evidence to suggest that increased dietary fiber intake would reduce the incidence or recurrence of adenomatous polyps within a two to four-year period.

Does fiber reduce the risk of heart disease?

But what about heart disease? Fiber is widely recommended as part of the “heart-healthy diet.” While fiber intake has been shown to improve glycemic control, a factor related to diabetes – a risk factor for heart disease – that fiber administration using psyllium has no effect and does not lower serum cholesterol. 

What about fiber and digestive issues like constipation and IBS?

If fiber acts like a broom in the colon, then shouldn’t it help with digestive issues like constipation and IBS? Should it accelerate transit to push matter to its inevitable exit? One systematic research review of 17 randomized controlled trials found that the treatment of IBS (irritable bowel syndrome) patients with fiber is controversial. 

The conclusion: “The benefits of fibre in the treatment of irritable bowel syndrome are marginal for global irritable bowel syndrome symptom improvement and irritable bowel syndrome-related constipation. Soluble and insoluble fibres have different effects on global irritable bowel syndrome symptoms.” Clinically, bran was no better than placebo in the relief of the overall symptoms of IBS and is possibly worse than a normal diet for some symptoms.


Is fiber beneficial? In some instances, like lowering blood sugar, yes, it can help. Is fiber necessary? No. Unfortunately, recommendations for high-fiber diets started with mere observations that confused association with causation and we can support our digestion with animal fats, butter being an excellent source of butyrate. Hopefully, these facts provide you with the information you need to move forward with an animal-based way of eating. 

Is Dietary Fiber Necessary For A Healthy Diet?

Dietary Fiber became a part of the public’s nutritional consciousness in the mid-1970s, when the newly released US Dietary Guidelines recommended that a healthy diet include plenty of “foods with adequate starch and fiber.” With that advice, along with the simultaneous ostracism of animal-based saturated fats, dietary fiber secured its place as a sacred component of mainstream nutritional wisdom.

Today, nearly 50 years later, most nutritionists still insist that plant fiber is necessary for optimal human health. But when we look more closely at what fiber does within the body, it becomes difficult to see how it provides any health benefit. With the health success that many people find with all-animal-product diets, fiber is being shown in a new light, and in most cases, it’s proving to be more a nuisance than a nutrient for human health.

A problem with discussing dietary fiber is that, on the surface, much of the conventional wisdom makes sense. The idea that ingesting a good amount of plant roughage to help “scrub” our intestines and colon to keep us regular and free of disease seems intuitive. The thought that we must keep our gut biome happy and well fed with a mix of soluble and insoluble fiber to assure gastrointestinal tract health sounds reasonable.

What is Dietary Fiber?
Simply put, fiber is the non-digestible part of plant foods. Common fiber types include cellulose, pectins, beta-glucans, and gums. Fiber is classified as soluble or insoluble based on whether it is dissolvable in water. Beans, oat bran, avocado, and berries are sources of soluble fiber; whole grains, wheat germ, beans, flax seeds, leafy vegetables, and nuts are sources of insoluble fiber. Animal-source foods, such as meat, seafood, eggs, and dairy, contain no fiber.

At a molecular level, plant fibers are chains of sugar molecules (polysaccharides) that our digestive tract can’t break down and that don’t offer any nutritional value to humans directly. Plant fibers pass through the stomach and end up in the small intestines intact, where they are either broken down and enjoyed by bacteria or pass through us unchanged. While the fiber-eating microbes in our gut are happy, they break down a small percentage of the rough plant materials for their own benefit, with no direct use to us.

Plant Fiber Myths
Fiber has multiple alleged mechanisms of health, but the impact of each is largely unsupported. Claims for dietary fiber’s preventative and healing powers include benefits for various illnesses and diseases, including constipation, colon cancer, diverticulosis, heart disease, diabetes, obesity, and more. Unfortunately, these wisdoms are based primarily on best-guess assumptions and epidemiological studies (studies that get data from patient or subject group questionnaires). Over the decades, there have been a few controlled scientific studies regarding dietary fiber, and the results fall short of conventional nutritional advice.

Is Fiber Needed to Cure Constipation?

The notion that humans need plant fiber for proper bowel function and intestinal health is false. Research regarding fiber and constipation shows that plant fiber does not lead to better outcomes; it often worsens things. While fiber does cause those with constipation to have larger bowel movements, it does not improve any of the unpleasant symptoms of constipation. Studies have shown that removing fiber from one’s diet can improve constipation. Many carnivorous mammals (and humans) have no problem whatsoever having normal, regular bowel movements in the complete or nearly complete absence of fiber.

Does Fiber Prevent Colon Cancer?

In line with the idea of scrubbing our insides for health, many believe that high fiber intake helps reduce the risk of colon cancer, but studies have proved this to be erroneous. The Nurses’ Health Study in 1999 followed 88,757 women over 16 years and found no significant benefit in reducing colon cancer risk. In 2000, a similar randomized study of high fiber intake also failed to show any reduction in precancerous lesions known as adenomas.

Can a High-Fiber Diet Heal Diverticulosis?

Diverticulosis is the pathological process that occurs when the innermost layer of the colon (the submucosa) protrudes through the outer muscular layer, forming small pockets that pouch out from the large bowel. A high-fiber diet and increased frequency of bowel movements are associated with a greater, rather than lower, prevalence of diverticulosis. Patients with IBS, Crohn’s disease, and ulcerative colitis all seem to respond similarly well to a reduced fiber diet.

Does Dietary Fiber Prevent Heart Disease?

The Diet and Reinfarction Trial in 1989 randomized 2,033 men to three different diets after their first heart attack. A standard, low-fat diet did not seem to reduce risk at all, and a high-fiber diet showed no benefit to cardiovascular health. The high-fat Mediterranean diet was shown to be beneficial. More recent trials such as the PREDIMED confirm the benefits of eating more natural fats such as meats, nuts, and olive oil. In all of these trials, the beneficial impact of fiber was essentially nonexistent.

Can Fiber Help Control Diabetes?

The role of fiber in insulin sensitivity and diabetes is open to debate. There is some evidence that dietary fiber can help, but only in indirect ways. High-fiber foods require more chewing, which may help to reduce food intake. Soluble fiber absorbs water to form a gel, further increasing the food’s volume, helping fill the stomach, and boosting satiety. Fiber bulks up food, decreases its energy density, and slows the body’s insulin response to carbohydrates. But we must remember that plant fiber from whole fruits, starchy vegetables, and grains usually comes with more sugars and carbohydrates, which are associated with poor glycemic control.

But Fiber Works for Other Animals

The animal kingdom’s ruminants, herbivores, and omnivores have evolved many ways to extract nutrients from plants and convert them to the building blocks needed for their growth and health. A cow’s stomach has multiple compartments, each with a highly specialized microbiome to break down and digest plant materials. Gorillas and other great apes have massive intestinal tracts and colons to deal with the nearly 40 pounds of plant material they eat daily — a volume that speaks to how little nutrition is in plant materials, even for a highly adapted herbivore. Cows and great apes graze and forage almost constantly throughout their waking hours. Yet even with these plant-digesting guts, the fiber mostly just passes on through. Cows, apes, and most all other herbivores produce a lot of waste!

Humans have small colons, comparatively short intestinal tracts, a small stomach, and a gut biome that is more suited to breaking down animal proteins and fats into building blocks we can use. If the need arises, humans can digest a limited range of plant foods (fruits, berries, nuts, roots, etc.) without issue. Still, the benefit — immediate energy availability — is small and certainly not required for long-term health.


So, is dietary fiber necessary for a healthy human diet? The answer is no. The goal of human nutrition is to provide our bodies with the energy and the structural components needed to build and maintain our animal-based cells — we don’t need anything from plants to accomplish these nutritional goals. Just because humans can ingest fiber-filled food, this ability in no way indicates that fiber is a nutritional health requirement. Much of the touted benefits of plant fiber have been based on erroneous assumptions and flawed epidemiological surveys. For these reasons, plant fiber should be regarded as unnecessary at best, and perhaps even harmful for many.

Carnivore and the art of pooping

Now let’s talk about fiber. The message we’ve heard for what seems like eons is, “If you don’t eat fiber, you can’t have a healthy bowel movement.” We’ve been told that fiber is essential for a healthy gut and healthy digestion; the latest word is that it’s necessary for a healthy microbiome. There are certainly studies and theories to support these assertions, but I can easily point out many observations that run completely contrary to those theories.

For instance, many carnivorous mammals have no problem whatsoever having normal, regular bowel movements in the complete or nearly complete absence of fiber. For example, my dogs poop on the grass every day despite eating nothing but meat. (I sometimes wish that lack of fiber would prevent them from pooping; then I wouldn’t always have to carry those little black dog poop bags every time I go out.) I know what you’re saying, and you’re right: Humans aren’t dogs, and we’re not carnivores (maybe), so perhaps we shouldn’t compare ourselves to dogs. But we can look to numerous human populations that have had no difficulties with elimination despite living on diets that are essentially devoid of fiber.

For example, I don’t recall the early Arctic explorers having to administer enemas to the Inuit populations when they arrived. Perhaps the handful of berries the Inuits would occasionally eat in the summer was sufficient for keeping them regular throughout the rest of the year. Instead of speculating, though, we can ask people today what happens when they go without fiber for a long period. The resounding response is that they have no problem whatsoever having bowel movements. They’re regular and comfortable, and most report their overall gastrointestinal function is the best it’s ever been in their lives. We have studies showing both that chronic constipation is relieved when the diet contains zero fiber and that people who eat lots of fiber have much higher rates of diverticular disease.

Why do we ignore these observations and instead rely on that good ol’ standby of nutritional epidemiology? Could it be because the origins of the nutrition field were tied to vegetarianism and a religious group that started feeding people cereal to cure them from having and acting on impure sexual thoughts? Companies like Kellogg’s and other grain-heavy megacompanies continue to influence nutritional organizations via funding of research and support of some of the dietitians’ groups.

The refrain is, “Eat your fiber, keep your colon nice and full, poop three times a day, and feed those fiber-starved little bacteria.” I’ve heard several prominent vegan proponents state that humans should have an average of three bowel movements per day and should expect to fart fairly frequently because it’s a normal state of affairs. They contend that early humans didn’t mind passing gas because they spent a lot of time outdoors. As far as I can tell, they pulled this theory out of their vegan asses. You will receive zero prizes at the end of your life for having had the largest bowel movements (in either size or quantity).

You shouldn’t be walking around with bloated guts and feeling the need to fart all day long. Why the hell would we have been designed to have a digestive system that caused us pain and discomfort? The short answer is that we weren’t. One of the most common “side effects” of a carnivore diet is the near-complete absence of gas. Yes, most people on an all-meat diet stop farting. I know some folks may find this fact a downside because they’re quite proud of the fact that they can level a room with relative ease via their methane retro cannon, but I hope most people consider the lack of gas to be an asset of the diet.

As I discussed earlier, fiber reportedly can lower cholesterol; that’s great, but I also mentioned that low cholesterol is linked to other conditions, such as dementia, depression, and perhaps cancer. Humans cannot digest fiber because our digestive tract wasn’t designed for fiber. Just because we shove fiber-filled foods down our digestive tube and some bacteria start to grow and eat it in no way indicates that our bodies require it. Think of it this way: If we were to start eating dirt, we’d have colons full of bacteria that prefer dirt. And if we believed that dirt was good for us, we could most likely find some compound that those dirt-eating bacteria produced that would be of benefit to us.

However, if we looked hard enough, we also could find compounds that were detrimental to us. Earlier, I talked about bias in research, and studies about dietary fiber are one place where we can see some bias. Some researchers believe that fiber is good for humans because of some crappy epidemiology. Therefore, they look for beneficial compounds that result from eating fiber while ignoring negative compounds. Can anyone say how a bunch of methane is benefiting our colon? What about the fact that fiber consumption has been shown to increases rates of diverticular disease, or that removing it from the diet often solves longstanding constipation?

Fiber can limit a glucose excursion; for example, if you drink apple juice, you see a fairly typical high spike in postprandial blood glucose, which arguably is a bad thing. If you eat a fiber-rich apple, you get a much lower spike. Well, guess what. If your diet is a bunch of meat, you also avoid large postprandial spikes of glucose. Why would Urk and the rest of our megafauna-munching ancestors have gone out of their way to eat a bunch of fibrous foods that would have provided next to no calories, would have been difficult to digest, and likely would have tasted like cardboard.

He didn’t have the American Diabetes Association telling him to eat his heart-healthy whole grains and leafy vegetables, which incidentally weren’t even cultivated yet. Urk was living it up on the bounty of fatty, delicious meat. From time to time he may have had something a little bit sweet, like some berries, but I can’t see him going out of his way to chew on super fibrous roots and bitter leaves unless he was desperate. I know I sure as hell wouldn’t have unless I’d had some overzealous dietitian yapping at me about phytonutrients, eating the rainbow, and the ill-defined balanced diet. How the hell do you make a balanced diet when you’re living through an ice age?

In the movie Jerry Maguire, you might remember that the athlete played by actor Cuba Gooding, Jr. repeatedly yelled, “SHOW ME THE MONEY!” during his contract negotiation. I bring that up here because I don’t see any evidence of the doom and gloom reports about poor gut function, scurvy, and micronutrient deficiencies when I look at the real-world application of the carnivore diet. So I have to say, “SHOW ME THE MONEY!” to all the critics. Results are what count.

When someone tells me that lack of fiber leads to poor gut health, I say, “How? Show me what the clinical consequences are.” All I see is people who report vastly improved digestion and often state that they feel the best they’ve felt in their lives. People with irritable bowel syndrome or inflammatory bowel disease tend to get better. If that’s the case, how does that translate to worsening gut health? I’m just a dumb ol’ MD, but that doesn’t seem to make sense to me.

My critics would point out that I’m citing anecdotes, the implication being that if anecdotal data doesn’t match our preconceived ideas, those reports must be discounted. How about we don’t discount this stuff and instead actually listen to our patients rather than our pharmaceutical sponsors?

The more I learn about nutrition, the more I’m convinced that is has its basis in religion as much as it does in science. Think about it: When people become passionate about diet, they often feel strong cultural and ethical emotions. I constantly am amazed at how certain camps get so entrenched about long-held beliefs of what’s healthy to eat. It’s very different than many other topics. For example, if we were to talk about the science of building furniture, most people wouldn’t get too excited because very few people are emotionally invested in whether something is made of cherry or maple. But when we talk about whether we should eat a steak or a big bowl of veggies, people become very animated.

Excerpted from The Carnivore Diet, By Dr. Shawn Baker.
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